The present invention relates generally to motorcycle drives and more particularly to chain drives for motorcycles utilizing chain deflecting mechanisms to minimize the effects of the drive on the rear wheel suspension.
Modern motorcycles, particularly those used for off-road purposes, commonly use a suspension system referred to as a trailing link or rear swing arm. With this suspension, the rear wheel is linked to the frame by a pivotal swing arm with a chain drive connecting the frame mounted engine to the rear wheel sprocket.
In this type of system, forces acting on the swing arm, including drive related forces, determine its position or angle with respect to the frame. It is an objective in the art, however, to achieve constant chain tension over the full range of swing arm travel and to minimize the effect of drive forces on the swing arm action. In the previously issued patent to Horst Leitner, U.S. Pat. No. 4,299,582, there has been described a certain chain deflecting mechanism rigidly secured to the swing arm and having dual chain sprockets spaced apart above and below the swing arm bearing to spread the chain and thereby affect chain tension during the motion of the swing arm. It has been the prevailing opinion in the industry, as exemplified by the abovecited patent, that a chain deflecting mechanism mounted to the swing arm provides the best isolation from drive interference with the suspension. Similarly, in U.S. Pat. No. 4,034,821, issued to Stoddard, et al., there are shown chain sprockets mounted to the swing arm and arranged to pinch the chain toward the swing arm to control the tension without regard to suspension compliance. However, Applicant's invention embodies the positioning of a chain deflecting means on the fixed frame to more effectively isolate the suspension from drive related forces. Particularly, mounting of chain deflecting rollers or sprockets to the frame at a location behind the swing arm pivot achieves the desired isolation. The exact coordinates for the location are dependent upon the dimensions of the drive train and vehicle geometry and can be ascertained mathematically.